ok scientists and ologists explain this one to me then

[planenut]

How bigs the universe?

I can remember back to when I was a yob (I can, really), I was having a heavy discussion with my younger sister when she asked a similar question; "how big is the Universe, how far does it go, what's at the end of it", then, poor girl, she just burst into tears. It truly is an unanswerable question, which therefore can be quite disturbing.

Think i'll put the kettle on!

 

[Thermo]

ohhh nooo boo hoo hoo hooo. Its got you all thinking deeply this one hasnt it! Ok how about this then. If a car is travelling down a dark tunnel at the speed of light and the driver turns on the headlights, will it have any effect?

 

[planenut]

Ah, I suspect "yes", as the speed of light will now be ""+ speed of car".

Yet, what if, the car is travelling east? Ha!

 

[Thermo]

im going out on a limb here but according to einstein the speed of light is constant so will it?

 

[hbark]

whats a woman doing watching traffic in a dark tunnel alone.
samaritans are only a phonecall away
by the way whats the braking distance for speed of light?!

 

[Panjandrum]

ohhh nooo boo hoo hoo hooo. Its got you all thinking deeply this one hasnt it! Ok how about this then. If a car is travelling down a dark tunnel at the speed of light and the driver turns on the headlights, will it have any effect?

From the perspective of an observer at the side of the tunnel, there will be a momentary flash of light, as the car passes, that illuminates the tunnel as far back as she can see. After the car passes, she will see the light disappearing away from her, with a significant red shift, the extent of which I can't be bothered to calculate. I rather suspect it would be shifted to a wavelength well beyond her ability to see - probably double the wavelength it would be if the car had not been moving at all.
She will, of course, have been sucked to oblivion by the passage of the car. So what she might have seen is purely hypothetical and irrelevant.
PJ

 

[Thermo]

dont be silly cars that go at the speed of light dont have a reverse gear. anyway youre not allowed to reverse in a tunnel. Im asking the questions here so no what ifs!!!!!!

 

[Panjandrum]

AARRGGHH Correction.
She would NOT experience the red shift effect because she would NOT see the headlights directly.
What she WOULD see is an instantaneous flash of reflected light from the side of the tunnel in the away direction.
Net effect, a flash of light from both directions.

 

[securespark]

Blimey, you lot! That's nearly as bad as the forest/ tree dilemma!

 

[ninebob]

My favourite teaser was always this old chestnut:

"What happens when an irresistable force meets an immovable object?"

I believe I have an answer for it BTW, which I will post if nobody else does...

 

[Thermo]

where did the women driver come from?????

 

[pipme]

Ok 45p
Conflicting with expectations, go read about it :-
http://www.bbc.co.uk/dna/h2g2/alabaster/A581096
Good old Beeb again !

 

[planenut]

where did the women driver come from?????

Let's not go there, how would she know? unless someone told her!
anyway, I thought the she was a pedestrian.......

but, just supposing, some passing motorist, travelling at the speed of light in a dark tunnel, flashes at a woman pedestrian?
Would she manage to get his number? in case she was pleased!

 

[Panjandrum]

In what kind of bizarre universe do you imagine any woman would be "pleased" by any man flashing any thing?

 

[hbark]

Flashing a wallet usualy perks the wife up a bit!